Language deficiencies have been shown to characterize dyslexic readers, but the nature of the relationship between language skill and reading failure remains obscure, leaving basic etiological questions unanswered. In a longitudinal design, the early language acquisition of children who, because of the incidence of dyslexia in their family backgrounds, are at risk for reading disability will be compared to that of a control group. The children's speech and behavior in naturalistic home settings has been videorecorded semiannually from the age of two years, and will be scored with respect to the amount, variety, and complexity of linguistic form, content, and function. Measures of cognition, play, and other developing abilities will supplement the record of each child's progress. All preschool records will be analyzed in relation to eventual reading achievement during elementary school. Various theories have proposed maturational lags, specific deficits, or stylistic differences in language development as the antecedent conditions for reading difficulties. These conflicting predictions about early differences between children who develop dyslexia and those who do not can be evaluated in the proposed study. Because the research will identify the developmental factors most predictive of later reading disorders, the results can provide a framework for the design of earlier intervention in the treatment of dyslexic children than is now possible.